Magnetic media are increasingly used for storing information according to a pattern of magnetic fields in a material on a substrate. Well-known examples include hard disk drives for computers, which store information on a rotating disk with a magnetic material with domains that are separately addressable to change a magnetic property of each domain according to the information to be stored, and MRAM, magnetoresistive random access memory, which stores information in cells defined by addressable magnetic domains whose polarity can be changed according to the information to be stored.
Magnetic media are generally made by depositing a layer of material having magnetic properties that may be easily changed through exposure to electric fields, magnetic fields, or electromagnetic fields. Domains are typically formed consisting of a low coercivity material surrounded by a higher coercivity material, so the magnetic properties in the domains of low coercivity may be readily changed. In this way, the polarity of a domain may be distinguished from that of its neighbor, and information can be stored and retrieved.
The substrates may be any structurally sound material, such as glass, aluminum, or plastic. The magnetic materials are generally metal alloys including metals such as cobalt, platinum, iron, manganese, nickel, chromium, vanadium, and the like. The magnetic material is often sputtered onto the substrate, sometimes over another material of high magnetic permeability, such as molybdenum or so-called “mu metal” to shield the magnetic pattern from the influence of other magnetic field sources nearby.
For some magnetic media, orientation of the magnetic domains is needed after they are formed. For example, to initialize an MRAM device to a null state, all the magnetic memory elements of the device must be aligned to the null state. Such alignment typically requires that the device be exposed to a magnetic field, usually with heat to increase mobility of the domains. Such processing is commonly done by disposing a batch of substrates having magnetic media surfaces in a furnace coupled to a large magnet. As the substrates are heated to a suitable mobility temperature, for example above the Curie temperature, a magnetic field is established within the chamber to align the magnetic domains of the substrates. The magnetic field strength typically used is above 0.5 T and sometimes as high as 10 T. Electromagnets are normally used, and superconducting magnets are normally used for the high field strengths. The magnets currently used are massive, requiring large power budgets and footprints to generate the fields needed. Such apparatus are quite expensive, and the furnaces employing such methods typically have low throughput preventing them from being commercially viable.
Thus, there is a continuing need for new apparatus and methods for magneto-thermal processing of substrates.